1. Field of the Invention
The invention relates to certain 2-substituted 5-chlorimidazoles, a process of preparing the 2-substituted 5-chlorimidazoles, and a process of converting some of the 2-substituted 5-chlorimidazoles to certain 2-substituted 5-chlorimidazole-4-carbaldehydes.
Several methods for the production of 2-substituted 5-chlorimidazole-4-carbaldehydes are known.
U.S. Pat. No. 4,355,040 describes a process according to which 2-amino-3,3-dichloroacrylonitrile is reacted with an aldehyde to the corresponding azomethine intemediate product and further with an hydrogen halide and water to the 2-substituted 5-haloimidazole-4-carbaldehyde. Experimental data is lacking in the patent. A great drawback of the synthesis is that the 2-amino-3,3-dichloroacrylonitrile used first has to be produced starting from dichloroacetonitrile by its readion with hydrogen cyanide/sodium cyanide. The extremely toxic reactors and the safety measures associated therewith that are already necessary for the preparation of the initial product, make the entire process unsuitable for industrial-scale production.
U.S. Pat. No. 4,355,040 discloses in another variant a 3-stage process, in which, in a first stage, an amidinehydrochloride is cyclized with high NH.sub.3 pressure with dihydroxyacetone, the imidazole alcohol is halogenated and finally oxidized to aldehyde.
It has turned out that pressures of over 20 bars are necessary for the cyclization reaction.
The oxidation of the alcohol works according to U.S. Pat. No. 4,355,040 in the presence of chromium oxide. It is obvious that an oxidation with heavy metal oxides, that are not recyclable as a rule, is no longer justifiable from present ecological aspects and requirements.